1. Technical Field
The present disclosure relates to electrosurgery. More particularly, the present disclosure relates to a logarithmic amplifier, an electrosurgical generator including the same, and a method of controlling an electrosurgical generator using the same.
2. Discussion of Related Art
Electrosurgery is the application of electricity and/or electromagnetic energy to cut, dissect, ablate, coagulate, cauterize, seal or otherwise treat biological tissue during a surgical procedure. Generally, electrosurgery utilizes an electrosurgical generator operable to output energy and active and return electrodes that are electrically connected via a cable assembly to the generator. The electrosurgical generator generates an electromagnetic wave (referred to herein as “electrosurgical energy”), typically above 100 kilohertz, between the active and return electrodes when applied to tissue. The electromagnetic wave created therebetween dissipates energy as heat as it travels between the electrodes. The electrosurgical energy usually has a frequency above 100 kilohertz to avoid muscle and/or nerve stimulation.
During electrosurgery, current generated by the electrosurgical generator is conducted through the patient's tissue disposed between the two electrodes. The current causes the tissue to heat up as the electromagnetic wave overcomes the tissue's impedance. Although many other variables affect the total heating of the tissue, usually more current density correlates to increased heating.
A variety of types of instruments utilizing electromagnetic radiation have been employed for various types of monopolar and bipolar electrosurgery. The basic purpose of both monopolar and bipolar electrosurgery is to produce heat to achieve the desired tissue/clinical effect. In monopolar electrosurgery, devices use an instrument with a single, active electrode to deliver energy from an electrosurgical generator to tissue, and a patient return electrode or pad that is attached externally to the patient (e.g., a plate positioned on the patient's thigh or back) as the means to complete the electrical circuit between the electrosurgical generator and the patient. When the electrosurgical energy is applied, the energy travels from the active electrode, to the surgical site, through the patient and to the return electrode. In bipolar electrosurgery, both the active electrode and return electrode functions are performed at the site of surgery. Bipolar electrosurgical devices include two electrodes that are located in proximity to one another for the application of current between their surfaces. Bipolar electrosurgical current travels from one electrode, through the intervening tissue to the other electrode to complete the electrical circuit. Bipolar instruments generally include end-effectors, such as grippers, cutters, forceps, dissectors and the like.
Electrosurgical generators apply various currents, voltages and frequencies to achieve various tissue effects. The current, voltage, and frequency may be varied to achieve a target tissue impedance, a target power, a target voltage, and the like. These target values are generally based upon the surgical procedure to be performed, tissue characteristics, and/or the desired tissue/clinical effect. Electrosurgical generators employ one or more control systems to achieve these target values and to prevent the electrosurgical generator from operating outside predetermined constraints.